Use escape for apostrophes that's understood by the parser

At the moment, apostrophes simply don't appear anywhere in posts. They're removed by the parser.

This is because `&apos;` doesn't seem to be understood by the used BBCode to HTML parsing library. `&apos;` [doesn't seem to be valid a HTML entity reference][1]. Using the apostrophe's unicode character `&#39;` instead fixes the issue.

[1]: http://fishbowl.pastiche.org/2003/07/01/the_curse_of_apos/